Analysis of key influencing factors on the bonding strength of bimetallic composite wear-resistant parts

The bimetallic composite wear-resistant parts achieve a balance between wear resistance and impact resistance by metallurgically combining high hardness wear-resistant materials with high toughness supporting materials. The core of its service reliability lies in the bonding strength between the two metal interfaces. Insufficient bonding strength will lead to early failures such as interface cracking and wear layer peeling. This article will systematically analyze the key factors that affect the bonding strength, covering the aspects of materials, processes, and quality control.

1、 Interface metallurgical bonding mechanism and strength composition

Bimetallic composite is mainly achieved through casting composite method, and its bonding strength is derived from:

Metallurgical bonding: During high-temperature casting, two metals undergo interdiffusion at the interface, forming a diffusion layer with a continuous transition between composition and structure. This is the ideal state for achieving high bonding strength.

Mechanical bite: By designing pre installed dovetail grooves, holes, and other structures, the bonding area and mechanical interlocking effect are increased.

Physical bonding: wetting and adhesion between liquid metal and solid metal surfaces.

Among them, metallurgical bonding is the core to achieve high-strength and high reliability bonding.

2、 Key factors affecting bonding strength

1. Material compatibility

Thermophysical performance matching: The linear expansion coefficients of the two materials should be as close as possible. Excessive differences can generate significant thermal stress during the cooling process and subsequent heat treatment, leading to cracks or even delamination at the interface.

Affinity of alloy elements: The alloy elements of the two materials should have good mutual solubility to promote the mutual diffusion of interface elements and form a stable transition layer. For example, the diffusion ability of elements such as carbon and chromium has a significant impact on the formation of gradient transition structures.

2. Interface pre-processing quality

Cleanliness: The surface of pre installed wear-resistant blocks (such as high chromium cast iron blocks) must be thoroughly cleaned of oxide scale, oil stains, moisture, and other pollutants. Any pollutant will form inclusions at the interface, becoming a weak point for bonding. Usually, sandblasting, acid washing, or mechanical processing are used to ensure surface activity.

Preheating temperature: It is crucial to fully preheat the preset block (usually to 400-600 ° C). This can prevent the "quenching" effect caused by excessive temperature difference when liquid metal comes into contact, avoid the formation of microcracks or white layers at the interface, and promote the flow and wetting of liquid metal.

3. Control of Casting Process Parameters

Pouring temperature: Liquid metal (usually high manganese steel or low carbon steel molten steel) needs to have sufficient superheat. The temperature is too low, the fluidity is poor, and the surface of the preset block cannot be fully wetted; Excessive temperature may exacerbate the melting and erosion of the preset block, alter its performance, and even lead to excessive dilution.

Pouring speed and method: It is necessary to ensure that the steel is filled horizontally and continuously to avoid turbulent flow scouring the pre-set blocks, which may cause displacement or damage to the surface cleaning layer. A reasonable pouring system design has a significant impact on achieving sequential solidification and reducing interface shrinkage.

4. Solidification process and subsequent heat treatment

Solidification sequence and shrinkage compensation: The design of the mold and riser should ensure that the composite solidifies in sequence from the wear-resistant layer to the ductile matrix, so that the interface area can be fully compensated to avoid shrinkage and porosity defects.

Heat treatment process: Heat treatment (such as water toughening treatment of high manganese steel) needs to consider the different phase transformation characteristics of the two materials. Improper control of temperature rise and fall speed can induce interface cracks due to the superposition of thermal stress. Standardized heat treatment helps to release some casting stresses and stabilize the interface structure.

3、 Combining quality detection and evaluation methods

To ensure reliability, multiple methods need to be used to indirectly or directly evaluate the bonding strength:

Non destructive testing:

Ultrasonic testing (UT) is a commonly used and effective method for detecting defects such as interface non fusion and large-scale shrinkage.

Color penetrant testing (PT): used to detect cracks that extend from the interface to the surface.

Damage detection and macro/micro analysis:

Macroscopic fracture analysis: Observe the morphology of the interface fracture through splitting or impact testing. The fracture surface with good metallurgical bonding is fibrous, and tear marks of two metals can be seen; When combined with poor areas, a smooth separation surface appears.

Metallographic examination: Prepare longitudinal metallographic specimens of the interface area and observe them under a microscope. The ideal interface should present a dense, continuous, inclusion free, and crack free microstructure, and be able to observe a certain width of element diffusion transition zone. This is the most direct technical basis for evaluating the combined quality.

Actual working condition verification: Trial use in specific areas, and infer the bonding quality by observing whether the wear-resistant layer peels off.

4、 Conclusion and Production Practice Tips

The bonding strength of bimetallic composite wear-resistant parts is a systematic quality index influenced by multiple factors coupling. Its control runs through the entire process of material design, pretreatment, melting and casting, heat treatment, and quality inspection.